The use of various thickening agents to provide increased body and viscosity to latex compositions is well known. These thickening agents include natural gums, soluble cellulose derivatives, and a variety of high molecular weight synthetic polymers such as the sodium polyacrylate thickeners.
To obtain more economical latex compositions and provide desired viscosity and adhesive character, it is known in the art that 10 to 20% by weight of starch based on latex polymer solids have been used in latex formulations. However, the use of gelatinized or pregelatinized starches has certain drawbacks due to rheological effects which occur on aging.
Starch pastes are labile to shearing and hydrolyzing influences and yield latex compositions which are quite variable in their rheological properties. Also, the manufacture of uniform dried pregelatinized starches is difficult. Partially swollen or cooked starch products are known in the prior art. Unfortunately, there appears to be difficulty in stopping the swelling process in water at the desired point of swelling. A cooked or partially cooked starch which has been heated in the presence of certain disintegration inhibitors is described in U.S. Pat. No. 2,127,372.
U.S. Pat. No. 3,067,064 discloses a thin-boiling, free-flowing starchy material prepared without additives which will not thicken on heating or gel on cooling. The applicability of this starch as a latex thickener is not disclosed. Indeed the thin-boiling properties disclosed would lead one to conclude otherwise. The viscosity is disclosed as being substantially the same before heating, during heating, and on cooling.
This invention provides novel and improved latex compositions which are indeed suitable for use as carpet backing adhesives and other textile applications and which employ an improved substantially non-birefringent cold water swelling granular starch composition as a thickener for latex in applications such as carpet backing adhesives. As will be shown more fully hereafter, the modified starch compositions of this invention and the novel latex compositions produced therewith unexpectedly exhibit superior rheological and cured film properties for application in the manufacture of textile laminated and white-backed rugs or carpets. These properties are achieved without the necessity of having to employ a ternary mixture of modified starch urea, and borax as is disclosed, for example, in U.S. Pat. No. 3,779,857.